| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a smoke detector having a structure in which, at a time of performing smoke detection, the S/N ratio of an output signal of a light receiving element is improved, to thereby accurately detect occurrence of fire. <P>SOLUTION: At both end portions of an optical case 21 having substantially cylindrical shape, a light emitting element 11 and a stray light portion 22 are arranged. In the stray light portion 22, a light trap 23 having curved surface is provided. Further, in the vicinity of the light emitting element 11, a condenser lens 24 is arranged to allow light L to incident on the curved surface of the light trap 23. At the time of smoke detection, light scattered by smoke particles in a smoke detection portion 25 is received by a light receiving element 12. However, the light incident on the light trap 23 is reflected on the curved surface a plurality of times to be attenuated in each reflection, so the light is not received by the light receiving element 12. Accordingly, the S/N ratio of an output signal S obtained from the light receiving element 12 is improved, thereby making it possible to accurately perform the smoke detection at an early stage. <P>COPYRIGHT: (C)2008,JPO&INPIT |
